The art of centrifugal clutches of the type and/or class here concerned with is old and highly developed.
While the details of construction of prior art clutches varies widely, the basic mechanical aspects and functions of such clutches has been substantially standardized.
The basic structure and mechanics that characterize prior art clutches includes an elongate central rotary power input shaft with front and rear ends and a plurality of axially spaced plates in rotary driving engagement about the shaft with the rearmost plate in fixed axial position on the shaft and the remainder of the plates being shiftable axially of the shaft; an elongate rotary power output part is engaged about the shaft and the plates; a plurality of axially spaced disks in rotary driving engagement and shiftable axially of the drive part are interengaged between the plates. The clutches are next provided with actuating means to normally yieldingly urge and hold the interengaged plates and disks out of frictional rotary driving engagement with each other when the clutch rotates at a low rate and to urge the plates and disks into driving frictional engagement with each other as the rate of rotation of the clutch is increased. The prior art actuating means include a large heavy flange-like carrier part carried by the shaft and spaced axially forward of the front plate; a plurality of circumferentially spaced spring means carried by the carrier part and coupled with the front plate to normally yielding urge the plate forward; and, a plurality of circumferentially spaced normally forwardly extending actuating weights pivotally carried by the carrier part on axes normal to radial planes on which the weights are positioned; and, normally radially outwardly and axially rearwardly projecting cam arms on the weights engaging a front surface of the front plate and operating to move that plate rearwardly, against the resistance of the spring means and to urge the several plates and disks into frictional driving engagement with each other and cause the output part to rotate with the shaft.
The above-noted basic prior art centrifugal clutch structure is shown in FIGS. 12 and 13 of the accompanying drawings.
Two notable prior art embodiments of the above prior art clutch structures are disclosed in U.S. Pat. No. 3,291,274, issued Dec. 13, 1966 to R. M. Wyman and entitled "Centrifugal Clutch"; and U.S. Pat. No. 4,111,291, issued Sep. 5, 1978 to G. F. Horstaman and entitled "Centrifugal Friction Mechanism."
The principal shortcoming of the above-noted prior art clutch structure resides in the necessity to provide a special carrier part to carry the spring means and the actuating means. Those special parts are costly, heavy and space-consuming. Of greater importance is the fact that the cam arms of the actuating weights slidably move radially inwardly and outwardly relative to their opposing surface of their adjacent related plate. The relative sliding movement between the weight cams and the plates occurs repeatedly to varying extent and under varying pressures during normal use and operation of the clutches. The movement between the weight cams and the plates creates frictional drag that slows and adversely affects operation of the clutches and often results in adverse wear of the parts that causes the clutches to "hang up" or otherwise fail to operate as intended.
The foregoing shortcomings that characterize most prior art centrifugal clutches of the character here concerned with have been accepted by the prior art as those disadvantages that must be incurred in exchange for the advantages that are sought to be attained through the use of such clutches.